Why was I charged for products in a different currency to the one I bought my Skype prepaid card with?

Why was I charged for products in a different currency to the one I bought my Skype prepaid card with?

When you buy a Skype prepaid card in a retail store, you are charged in the local currency. However, in your Skype account, you can only choose a limited number of currencies to buy Skype products with. If we don't support the currency you purchased the Skype prepaid card with, we’ll simply convert the value of your card to a usable currency. This happens when you redeem the card in your Skype account.